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AN INTERESTING ROOF ADDS COMPLEXITY AND TIME TO THE BUILD Visually, the ProHOME’s dormered roofline defines the house. The large gable dormer creates the space for the large master bathroom, while the shed dormer accommodates the other full bath and the laundry room. The low eaves across the front of the house create a horizontal emphasis, reducing the scale of the house and creating a comfortable entry. Maines used the combination of dormer styles to evoke several architectural styles—Victorian, farmhouse, and the venerable Cape— that figure prominently in the local housing stock. For all its design elegance, however, the roof will be an epic framing job. Guertin figures the second-floor ceiling and roof will take about two-thirds of the framing time for the entire house. The two dormers, each with a different roof pitch, create an irregular valley and add complexity to the framing. Using TJIs for the ceiling joists and rafters takes more time; they are more cumbersome to cut than dimensional lumber, and both the joist and the rafter webs have to be padded out at the eaves so that these offset framing members can be screwed together. Despite the added steps, TJIs have some distinct advantages: They are straight and don’t shrink, twist, or crack—and they’re light, an advantage any carpenter will appreciate. With a vented roof assembly and a deep blanket of blown-in insulation, insulation baffles are necessary to maintain an airspace along the eaves and at the shed dormer roof. The underside of the I-joists’ top flange is a convenient place for Guertin to fasten insulation baffles that he’ll make from rigid polyisocyanurate insulation. This ensures a clear air path between the continuous Cor-A-Vent soffit and ridge vents. And because of their thin OSB webs, TJIs also have limited thermal bridging compared to dimensional lumber, so they improve thermal performance along the eaves where thermal bridging could occur. Instead of installing blocking between the rafters at the eaves, a continuous LSL rim board runs along the outer edge of the top plate and braces the MAXIMIZING SOLAR PRODUCTION An important part of the roof plan is the photovoltaic panels. While there are no structural concerns for adding a PV array to this roof system, Maines took several steps to optimize the roof for an array. With a two-story eave on one side and a one-story eave on the other, the house is essentially a saltbox. Orienting the two-story facade with the unbroken roof plane to the rear for southern exposure was important to accommodate the 12kw array needed for net zero. Consolidating all of the plumbing into a single vent stack maximized the usable area. While a steep roof was desirable for aesthetic reasons, the 10-in-12 roof pitch—between the ideals for summer and winter—was chosen to maximize production over the course of the year. 74 FINE HOMEBUILDING